Antibiotic U-64,815 can be differentiated from the known related antibiotics kijanimicin [A. K. Mallams, et al., J. Amer. Chem. Soc. 103, 3938, 3940 (1981)], antlermicins [K. Kobinata, et al., J. Antibiotics 33, 244 (1980); K. Isono, et al., ibid., 33, 772 (1980)] and tetrocarcins [F. Tomita, et al., J. Antibiotics 33, 668 (1980); T. Tamaoki, et al., ibid., 33, 946 (1980)] on the basis of observed .sup.13 C magnetic resonance spectra. Compound 12 disclosed in the J.A.C.S. article, appears to be identical to antibiotic U-64,815. Final resolution of this identity is in progress.